Modacrylic fiber is a manufactured fiber in which the fiber forming substance is any long chain synthetic polymer composed of less than 84% but at least 50% by weight of acrylonitrile units. (-CH2CH[CN]-)x. Modacrylic fibers are made from resins that are copolymers (combinations) of acrylonitrile and other materials, such as vinyl chloride, vinylidene chloride or vinyl bromide.

What are the differences and similarities between acrylic and modacrylic fibers?

Like acrylic fibers, modacrylic fibers are made from acrylonitriles. However, more polymers of other types are added to make the copolymers of modacrylics.

Acrylic fibers are stronger than modacrylic fibers, but modacrylics are adequately durable for their end uses.

Modacrylics have better heat retention and are flame retardant. Acrylic fibers do not have these properties.